Measuring harmonic distortion in electrical power networks – New approach

Standard specification for power network quality diagnostic systems requires synchronization of sampling rate to the network frequency in every 10 s in order to ensure high accuracy of harmonic analysis. The total harmonic distortion (THD) cumulates measurement errors, therefore it is the most sensitive parameter to the frequency synchronization. This paper investigates two main effects putting impact on the THD computation accuracy. The first is the effect of the base clock rate of sampling hardware and the second is the practical deviation of network frequency during the 10 s synchronization period. The relative accuracy of THD calculation is examined in different real practical solutions and different synchronization methods are discussed and assessed. Theoretical proof and practical demonstration are given to show the needs of special synchronization methods in certain measuring circumstances.